I think a diesel is exactly what the Porsche Cayenne needs. The hybrid Cayenne will get better fuel economy within the city, but once you leave town the heavy and overpowered Cayenne will guzzle fuel like nobody's business.

A few years ago a diesel engine in sports car would seem unacceptable. Not anymore. Various diesel-powered sports sedans in Europe, notably from BMW as well as the Audi TDI LeMans victories have quickly changed that image for good. Porsche has access to great diesel engines (Audi/VW), so why not? They could get the current V6 TDI and V10 TDI from the Touareg and modify them in output, performance and character to suit the Cayenne. And you'd still get better fuel economy than with a comparable gasoline engine.